1. Field of the invention
This invention relates to a method of forming nanostructured carbons and particularly, a method of forming said materials easily and quickly.
2. Description of the Related Art
Recently, a lot of researches and studies have been made on nanostructured carbons on the order of a few nanometers (nm) in diameter such as carbon nanotubes, carbon nanofibers, and graphite nanofibers. A carbon nanotube is a seamless tube made by wrapping a single planar sheet (called a graphene sheet) of 6-carbon rings. A single wall nanotube is made of a single graphene sheet. A multi-wall nanotube is made of a plurality of graphene sheets wrapped in a nested structure. Graphite nanofibers are composed of cylindrically laminated graphene sheets whose ends are cut into cone-shapes or integration of small pieces of graphene sheets aligned to the surfaces of catalyst metals used to produce the fibers.
When an electric field of a threshold value or greater is applied to a metal or semiconductor that is placed in a vacuum chamber, electrons pass through an energy barrier near the surface of the metal or semiconductor due to the quantum tunnel effect and as the result, electrons are emitted in vacuum even at ordinary temperatures. This electron emission due to this principle is called a cold cathode electron emission or simply called a field mission.
As the nanostructured carbons are excellent in various performances such as electron emission characteristic, heat resistance, and chemical stability, they have been expected to be employed as electron emission sources that apply the above electron emission principle to image display. Further, as the nanostructured carbons can also work as semiconductors and electric conductors, they have been expected to work as electric and electronic devices.
Conventionally, nanostructured carbons have been formed by the arc discharge process, thermal chemical vapor deposition (CVD) process, vacuum plasma process, or the like. For example, Japanese Non-Examined Patent Publication 2002-115071 discloses a method comprising steps of heat-treating a substrate having a thin catalyst metal film in vacuum and forming thin graphite nanofiber films on designated areas of the substrate selectively by the thermal chemical vapor deposition (CVD) process. Japanese Non-Examined Patent Publication 2001-64775 discloses a method of producing vertically-oriented carbon nanotubes on a substrate by modulating the output of a microwave by the time to generate plasma in a vacuum film-forming chamber.
The conventional arc-discharge and vacuum-plasma processes for forming nanostructured carbons respectively require a facility to vacuumize the equipment. This makes the equipment complicated and increases the equipment expenses and production costs. Further, the arc-discharge process is hard to make nanostructured carbons directly grown on a planar substrate. The processes can directly form nanostructured carbons only locally but cannot form them directly on a wide substrate at all. Furthermore, the rate of forming nanostructured carbons is very small which is assumed that the gas concentration is very low because the reaction is carried out in vacuum. Meanwhile, as the thermal CVD process must decompose the raw material by heat, the production temperature is very high (450 to 600° C.). Therefore, the substrates on which nanostructured carbons are to be directly formed must be very heat resistant and they are limited to ceramics and quartz glass. Naturally, this process is not applicable to substrates of ordinary glasses such as soda glasses and low alkali glasses (including non-alkali glasses) and plastic substrates.